The subject of the present invention is a thermal contact breaker for printed circuit board.
U.S. Pat. No. 3,321,597 describes a thermal contact breaker of the type including a slider within a housing. A sudden action bimetal strip above the slider, is connected to a terminal of a power circuit, and bears a moving contact. A fixed contact lying opposite the moveable one, is connected to the second terminal of the power circuit. The slider includes a window through which the moving contact can extend to contact the fixed contact and axially immobilize the slider. Excessive current through the bimetal strip causes it to lift the moveable contact and allow the slider to move to its tripped position under the force of a spring. The slider then prevents engagement of the contacts.
The contact breaker described in the above patent is desirable especially because it is of the free tripping type, in that the power circuit continues to be protected even when the reset button is held in its engaged position. However, the contact breaker is too large to allow it to be fitted to printed circuit boards in mass production, and its structure does not permit easy fitting thereof.
U.S. Pat. No. 4,068,203 describes a thermal contact breaker of the same type in which the slider separates the housing into two longitudinal chambers inside one of which is arranged a bimetal strip of the Taylor type described generally in the document GB-B-657,434 which produces excellent tripping performance in the case of overvoltage. However, this U.S. patent describes a contact breaker of very large size which does not allow its inclusion on a printed circuit board and whose internal structure is particularly complex and costly to produce.
The document FR-A-2,543,734 describes a thermal contact breaker of small size for printed circuit boards which includes two fixed terminals of a power circuit as well as a fixed contact of a signaling circuit. However, the signaling circuit is not electrically isolated from the power circuit since it uses one terminal of the latter in the case of tripping of the contact breaker. In addition, unlike the device described in the first two documents mentioned above, this contact breaker is not of the free tripping type.